Glaucoma affects millions in the US and is the second leading cause of blindness worldwide. While surgical and pharmacologic approaches to reduce intraocular pressure can be beneficial, a recently convened NEI strategic planning group explicitly recommended focused research on retinal ganglion cell neuroprotection. One novel approach in this regard is the activation, by preconditioning, of robustly powerful survival mechanisms endogenous to the cell. We were the first to demonstrate in rodents that brief exposures to noninjurious ischemia or hypoxia promote near complete protection of the retina from ischemic injury. We now show in a mouse model of experimental glaucoma that long-lasting phenotypic changes induced by repetitive preconditioning with hypoxia, prior to intraocular hypertension, can prevent ganglion cell death. Studies proposed herein will utilize inducible and retina-specific knockout and transgenic mice to begin to elucidate the mechanistic basis of this innate protective response we have termed glaucoma tolerance. Specific Aim 1: Elucidate the role of the hypoxia-inducible transcription factor HIF-11 in mediating changes in gene expression responsible for glaucoma tolerance. Hypothesis: Ganglion cell protection following repetitive hypoxic preconditioning results from a unique expression profile for HIF-11 that leads to the long-lasting expression of heme oxygenase-1 and other survival-promoting HIF-11 gene targets. Specific Aim 2: Determine how nitric oxide modulates the ability of repetitive hypoxic preconditioning to promote glaucoma tolerance. Hypothesis: Activation of the constitutive nitric oxide synthase isoforms by repetitive hypoxic preconditioning is necessary for induction of a long-lasting cytoprotective phenotype by facilitating HIF-11-mediated and CREB-mediated transcription of cytoprotective genes. Specific Aim 3: Establish the mechanisms whereby glaucoma tolerance is achieved as a result of hypoxic preconditioning-induced activation of pAkt (protein kinase B)-dependent survival pathways. Hypothesis: Repetitive hypoxic preconditioning promotes pAkt stabilization and, subsequently, the prolonged phosphorylation of several anti-apoptotic effectors that contribute to glaucoma tolerance. The endogenous mechanisms of ganglion cell protection identified in this research program may provide novel therapeutic targets for preventing or reducing optic neuropathy in glaucoma. Ganglion cell death in glaucoma is responsible for devastating vision loss in millions of individuals. Our work provides a new approach to ganglion cell protection: Applying stress stimuli that activate endogenous mechanisms of gene expression to promote ganglion cell survival. Elucidation of the molecular basis of these innate cytoprotective pathways will yield a unique category of prevention and treatment strategies for the high-risk glaucoma population.